Bonnet Carre opens; Corps says more water in Atchafalaya would be 'devastating'

As the Army Corps of Engineers announced a partial opening of the Bonnet Carré Spillway on Friday, a Corps officer said new predictions indicate the Atchafalaya River at Morgan City will rise during this flood event to a level that would be nearly a foot over the moderate flood stage and about one-third foot of the March 2019 crest.

The news came as at least one Mississippi official urged the Corps to consider opening the Morganza Floodway as an alternative to the Bonnet Carré, sending even more water into the Atchafalaya system.

Putting more water into the Atchafalaya would result "in even more stress on Morgan City and all the communities surrounding it," said Col. Stephen Murphy of the Corps at Friday's event marking the opening of the Bonnet Carré. "More water in the Atchafalaya would be absolutely devastating."

At 7 p.m. Friday, the Mississippi River at the Carrollton Street gauge in New Orleans was at 16.32 feet and expected to rise to the 17.0-foot flood stage Wednesday and stay there until at least until April 16, according to the National Weather Service

Earlier this week, a sudden rise in the river crest forecast led the Corps to conclude that the river's flow at New Orleans would reach the 1.25 million cubic feet per second trigger for opening the Bonnet Carré. That spillway diverts water from the river into Lake Pontchartrain and down to the Mississippi coast.

At Friday's Bonnet Carré opening, Murphy said the Corps plans to open 10 or 20 of the spillway's 350 bays at a time over a four-week period, probably to a maximum of 95-110 bays. The Corps anticipates a maximum flow of 120,000-130,000 cubic feet per second for about a week. He anticipates that the water directed toward Mississippi would amount to only about 10% of last year's total.

"To the people affected by the opening of the spillway," said Gen. Mark Toy, commander of the Corps' Mississippi Valley Division, "I ask you to understand that we do this to help save lives, to protect people."

But some Mississippi state officials may not be in an understanding mood.

This will mark the third consecutive year the Bonnet Carré has been opened, a first in the spillway's eight-decade history. Last year was the first time the spillway was opened twice in the same year.

Mississippi officials, environmentalists and other stakeholders filed a federal lawsuit in December alleging that the Corps failed to consult with parties in that state before opening the spillway and subjecting Mississippi to flooding, loss of income from saltwater fisheries and ecological damage.

The Biloxi Sun Herald quoted a spokesman for Mississippi Secretary of State Michael Watson as saying this during an online meeting of stakeholders:

“The Mississippi Gulf Sound is still reeling from the 3 openings in the past two years and these impacts still haven’t been adequately measured or considered, yet you’re about to make it even worse by again using the BCS this year.

“While you claim you do not have the authority, have you even requested a change in operating guidelines to help diminish those impacts by at least allowing a partial opening of the Morganza?”

At Friday's spillway opening, Toy said, "When we open the spillway, we do everything we can to help mitigate its impact."

At 8 p.m. Friday, the Atchafalaya River at Morgan City was at 6.89 feet. At 6.0 feet, the river causes minor flooding between the flood walls in Morgan City and Berwick. At 7.0 feet, the flooding is rated as moderate. The National Weather Service forecast says the river will rise to 7.5 feet Wednesday.

The one-foot rise Murphy talked about would take the river to about 7.9 feet.

Last year, one of the worst for flooding in recent years, Hurricane Barry's storm surge pushed the river to 10 feet in July. Otherwise, the 2019 crest came March 15, when the river reached 8.25 feet, according to the National Weather Service.

The 2019 flooding persisted from later winter into the summer, threatening homes in the Stephensville area and covering portions of La. 70 with water in lower St. Martin. Shrimpers said the influx of freshwater hurt their catch, and sediment deposited in the system led to shoaling in important commercial waterways.

To combat the back-flooding along Bayou Chene, the St. Mary Levee District and other agencies sank a barge in the bayou at a cost of millions. A permanent structure is under construction at a cost of $80 million.

By congressional mandate, the Old River flood control structure diverts 30% of the Mississippi River's water into the Atchafalaya system